System and method for estimating terminal position based on non-geostationary communication satellite signals

Abstract

A device is provided for use with a satellite and a receiver having a local oscillator. The satellite is traveling in a vector and transmits a signal having an expected frequency. The receiver receives a received signal having a received signal frequency. The device includes: a Doppler shift measuring portion measuring a Doppler shift D m ; a predetermined Doppler shift storage portion storing a predetermined received Doppler shift D p ; a received signal Doppler shift error calculating portion calculating a received signal Doppler shift error D e ; a predetermined receiver position storage portion storing a predetermined position P p of the receiver; and a receiver position estimating portion calculating an estimated receiver position P e based on the predetermined position P p of the receiver and the received signal Doppler shift error D e .

What is claimed as new and desired to be protected by Letters Patent of the United States is: 
     
       1. A device comprising:
 a receiver configured to receive ephemeris and time information regarding a communications satellite, and to receive a signal transmitted from the satellite, wherein the ephemeris information reflects velocity and direction data regarding the satellite; 
 a Doppler shift calculator configured to determine an expected Doppler shift D p  and a measured Doppler shift D m  based on the ephemeris information, a last known position of the device and the received signal; 
 a Doppler shift error calculator configured to determine a Doppler shift error D e  based on the expected Doppler shift D p  and the measured Doppler shift D m ; and 
 a position calculator configured to determine a predetermined position P p  of the device based on the ephemeris information and the last known position of the device, and to determine an estimated change in distance P e  of the device, along a maximum effect vector from the predetermined position P p , based on the predetermined position P p  and the Doppler shift error D e . 
 
     
     
       2. The device according to  claim 1 , wherein the Doppler shift error is determined as D e =D p −D m . 
     
     
       3. The device according to  claim 2 , wherein the estimated change in distance of the device is determined as P e =P p +(K 2 ×D e ), wherein K 2  is a predetermined value associated with a position estimation loop. 
     
     
       4. The device according to  claim 1 , further comprising:
 a frequency calculator configured to determine a frequency correction factor f e , for correcting a local oscillator frequency, based on a predetermined oscillator frequency f p  and the Doppler shift error D e . 
 
     
     
       5. The device according to  claim 4 , wherein the Doppler shift error is determined as D e =D p −D m . 
     
     
       6. The device according to  claim 5 , wherein the frequency correction factor is determined as f e =f p +(K 1 ×D e ), wherein K 1  is a predetermined value associated with a frequency estimation loop of the device. 
     
     
       7. The device according to  claim 5 , wherein the estimated change in distance of the device is determined as P e =P p +(K 2 ×D e ), wherein K 2  is a predetermined value associated with a position estimation loop of the device. 
     
     
       8. The device according to  claim 7 , wherein the frequency correction factor is determined as f e =f p +(K 1 ×D e ), wherein K 1  is a predetermined value associated with a frequency estimation loop of the device. 
     
     
       9. A method comprising:
 receiving, by a satellite terminal (ST), ephemeris and time information regarding a communications satellite, and receiving a signal transmitted from the satellite, wherein the ephemeris information reflects velocity and direction data regarding the satellite; 
 determining an expected Doppler shift D p  and a measured Doppler shift D m  based on the ephemeris information, a last known position of the ST and the received signal; 
 determining a Doppler shift error D e  based on the expected Doppler shift D p  and the measured Doppler shift D m ; and 
 determining a predetermined position P p  of the ST based on the ephemeris information and the last known position of the ST, and determining an estimated change in distance P e  of the ST, along a maximum effect vector from the predetermined position P p , based on the predetermined position P p  and the Doppler shift error D e . 
 
     
     
       10. The method according to  claim 9 , wherein the Doppler shift error is determined as D e =D p −D m . 
     
     
       11. The method according to  claim 10 , wherein the estimated change in distance of the ST is determined as P e =P p +(K 2 ×D e ), wherein K 2  is a predetermined value associated with a position estimation loop. 
     
     
       12. The method according to  claim 9 , further comprising:
 a frequency calculator configured to determine a frequency correction factor f e , for correcting a local oscillator frequency, based on a predetermined oscillator frequency f p  and the Doppler shift error D e . 
 
     
     
       13. The method according to  claim 12 , wherein the Doppler shift error is determined as D e =D p −D m . 
     
     
       14. The method according to  claim 12 , wherein the frequency correction factor is determined as f e =f p +(K 1 ×D e ), wherein K 1  is a predetermined value associated with a frequency estimation loop of the ST. 
     
     
       15. The method according to  claim 13 , wherein the estimated change in distance of the ST is determined as P e =P p +(K 2 ×D e ), wherein K 2  is a predetermined value associated with a position estimation loop of the ST. 
     
     
       16. The method according to  claim 15 , wherein the frequency correction factor is determined as f e =f p +(K 1 ×D e ), wherein K 1  is a predetermined value associated with a frequency estimation loop of the ST.